Power conversion system with a DC to DC boost converter

ABSTRACT

A voltage booster allowing for increased utilization of low voltage, high current, unregulated DC power (“LVDC source”), such as, but not limited to, fuel cells, batteries, solar cells, wind turbines, and hydro-turbines. LVDC generation systems employing a variable low voltage DC-DC converter of the present disclosure may be used without a power inverter in applications requiring high voltage DC inputs and can also allow for the employment of common, low cost, reliable, low voltage energy storage chemistries (operating in the 12-48 VDC range) while continuing to employ the use of traditional inverters designed for high voltage power supplies. An embodiment of the DC boost converter includes a plurality of interleaved, isolated, full-bridge DC-DC converters arranged in a Delta-Wye configuration and a multi-leg bridge.

RELATED APPLICATION DATA

This application claims the benefit of priority of U.S. ProvisionalPatent Application No. 61/781,965, filed Mar. 14, 2013, and titled PowerConversion System with a DC to DC Boost Converter which is incorporatedby reference herein in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of powerelectronics. In particular, the present invention is directed to a PowerConversion System with a DC to DC Boost Converter for variable lowvoltage DC power sources and high voltage DC loads.

BACKGROUND

There are many devices that either produce variable low voltage DC power(below 100 VDC) or require low voltage DC power. A common example of alow voltage DC power source is a fuel cell, which is an electrochemicaldevice which reacts hydrogen with oxygen to produce electricity andwater. The basic process is highly efficient, and fuel cells fueleddirectly by hydrogen are substantially pollution free. Yet, the outputof fuel cells (variable low voltage, high current DC power) makesefficient engineering solutions difficult, especially in residential andlight commercial applications, where the power output demands of a fuelcell are not as significant. While sophisticated balance-of-plantsystems are used for optimizing and maintaining relatively low powercapacity applications, they do not effectively meet residential andlight commercial power needs and at least a portion of this failure isattributable to the lack of effective power electronics to pair with lowvoltage DC power sources and loads.

For some low voltage DC sources such as fuel cells and batteries, thepower conversion efficiency degrades over time as the sources aredepleted. For example, for fuel cells, the fuel cell stack producesvariable low-voltage DC based on power demand and the stack's averagevoltage degrades over time based on catalyst loss and energy conversionefficiency degradation. Increasing the number of fuel cells running inparallel will increase the output stack voltage, but degradation willstill render the system inefficient and possibly unusable in arelatively short amount of time, requiring that the fuel cell stack bereplaced.

SUMMARY

In a first exemplary aspect, a DC to DC boost converter (DDBC) forconverting power received from a variable, low voltage DC source, theDDBC comprises a plurality of interleaved, isolated, full-bridge DC-DCconverters arranged in a Delta-Wye configuration and a multi-leg bridge.

In another exemplary aspect, a power conversion system has a powerrating, and the power conversion system comprises a low voltage powersource having an initial output voltage, a DC-DC boost converter (DDBC)coupled to the power source, and an inverter coupled to the DC-DC boostconverter, wherein the DDBC is designed and configured to provide acontinuous output current, a voltage ratio less than one, and to receivea discontinuous input current.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, the drawings show aspectsof one or more embodiments of the invention. However, it should beunderstood that the present invention is not limited to the precisearrangements and instrumentalities shown in the drawings, wherein:

FIG. 1 is a graph of commercial inverter efficiency versus loadpercentage for DC sources;

FIG. 2 is a block diagram of a power conversion system according to anembodiment of the present invention;

FIG. 3 is a block diagram of another power conversion system accordingto an embodiment of the present invention;

FIG. 4 is a block diagram of another power conversion system accordingto an embodiment of the present invention;

FIG. 5 is an electrical schematic of a DC to DC (DC-DC) boost converteraccording to an embodiment of the present invention;

FIG. 6 is a process diagram of providing high voltage DC power to a loadfrom a low voltage DC power source; and

FIG. 7 is a block diagram of a computing system suitable for use with aDC-DC boost converter according to embodiments of the present invention.

DESCRIPTION OF THE DISCLOSURE

There are many DC power sources that produce low voltage, high current,unregulated DC power (“LVDC source”). However, many of these LVDCsources are relatively incompatible with commercially availableinverters insofar as their efficiencies and usefulness are impeded bythe high input voltage required for efficient operation of these typesof inverters. As an example of this phenomenon, FIG. 1 shows a graph 10of inverter efficiency versus load percentage for a solar power source,i.e., a high voltage source, and a LVDC source, where a traditionalinverter is used, i.e., one typically designed to receive high voltageinputs. As shown, the power conversion efficiency of power coming fromthe solar source varies as a function of load and is represented bysolar voltage input 14. Solar voltage input 14 reaches a maximum, inthis example, of about 93% conversion at between about 50 and 75 percentof maximum load. In comparison, the power conversion efficiency of theLVDC source at its beginning of life (BOL) (represented by BOL voltageinput 18) is considerably less. At its peak, the LVDC source obtains anefficiency of about 85% at between about 65 and 75 percent of maximumload. Moreover, as the LVDC source ages, there is an even greaterdisparity in power conversion when compared to the solar source. At theend of life (EOL) of LVDC sources, the power conversion efficiency peaksat about 70% at 70% maximum load.

The differences between the voltage inputs are designated as loss areas26, i.e., loss area 26A and B, and represent inefficiencies inconversion of power. Loss area 26A is the difference between solarvoltage input 14 and BOL voltage input 18 and loss area 26B is thedifference between solar voltage input 14 and EOL voltage input 22. Lossarea 26B is greater than loss area 26A because while solar voltage input14 may decrease over time, the longevity of the solar source farsurpasses that of LVDC power sources, such as batteries and fuel cells.The difference between BOL voltage input 18 and EOL voltage input 22 islargely due to the decreased ability for the LVDC source to generatesufficiently high output voltages to reduce inefficiencies related tothe use of inverters designed for high voltage power sources.

A variable low voltage DC-DC converter according to present disclosureallows for improved and increased use of numerous power sources, suchas, but not limited to, fuel cells, batteries, solar cells, windturbines, and hydro-turbines. The variable low voltage DC-DC converterallows for optimization of a distributed generation system including aLVDC source and an energy storage device for efficiency, life expectancyand cost without being limited to high voltage outputs from the LVDCsource. LVDC generation systems employing a variable low voltage DC-DCconverter of the present disclosure may be used without a power inverterin applications requiring high voltage DC inputs, such as a vehicle orother battery charger, a heater, a welder, a motor starter, a motor, ahigh voltage DC (HVDC) utility application, a telecommunicationsequipment, a vehicle, a tractor, a marine auxiliary power, and amaterial handling equipment. A variable low voltage DC-DC converteraccording to the present disclosure can also allow for the employment ofcommon, low cost, reliable, low voltage energy storage chemistries(operating in the 12-48 VDC range) while continuing to employ the use oftraditional inverters designed for high voltage power supplies. Thevariable low voltage DC-DC converter also can simplify the design (byreducing components required) and increase the useful life of the LVDCsources while allowing for efficient charging and discharging to a highvoltage DC application.

Additionally, incorporating LVDC power storage with highly efficientgenerating sources such as fuel cells, solar or wind increases theeconomic viability of the generating device by capturing more useableenergy and allowing for the use of low cost LVDC power storage employingbatteries technologies, such as lead acid batteries. For example,vehicle and residential energy storage systems are dominated by batterychemistries allowing for high voltage storage topologies. Lithium-ionand nickel-metal-hydride are two examples of batteries that operate inthe 400-600 VDC range so as to ensure high voltage DC output tocommercially available inverters for high efficiency conversion. Highvoltage storage topologies are expensive and can only accept power atcertain voltages. Use of a variable low voltage DC-DC converter allowsfor use of produced power at lower voltages to be stored within thebatteries as well as the use of lower cost batteries, such as lead acid.

Referring now to FIG. 2, a high-level block diagram of a powerconversion system 100 is shown that converts a variable low DC voltagefrom a DC source 104 into an AC voltage for an AC load 108. Examples ofa DC source 104 can include a variety of variable DC power sources thatare typically subject to low voltage cutoffs, such as, but not limitedto, a solar array, a wind turbine, a fuel cell, a water turbine, abattery, and a capacitor. Examples of AC load 108 include, but are notlimited to, an electric power grid, a vehicle, and a residence.

As shown in FIG. 2, power conversion system 100 includes a DC-DC boostconverter (DDBC) 120, an inverter 124, and a control system 128. Asdescribed in more detail below with reference to FIG. 3, DDBC 120converts variable, low voltage DC to constant, high voltage DC using thehigh current output of the DC source 104. Once converted to fixed, highvoltage DC, the voltage is delivered to inverter 124, which converts theDC voltage to an AC voltage suitable for distribution to AC load 108.The operation of DDBC 120 is regulated by control system 128 that, at ahigh level controls, among other things, the input current level and aset-point for inverter 124 so as to draw power from the DC source.Control system 128 is described in more detail below with respect toFIG. 4.

FIG. 3 shows an alternative embodiment of power conversion system 200employing a DDBC 120. In this embodiment, power conversion system 200 isdesigned and configured so as to receive power from both a DC source,i.e., DC source 104, and an AC power source 208 (e.g., the electricalgrid). DDBC 120 receives inputs from DC source 104 and AC power source208 (via inverter 212) and converts the inputs to a low, high current,DC voltage for a low DC voltage storage/load 204. Examples of low DCvoltage storage/load 208 include, but are not limited to, an electricvehicle, a material handling equipment (e.g., electric fork-lifts), atractor, a marine auxiliary power system, and a telecommunicationsequipment.

As is well known, a DC to DC converter is a species of power converter.Moreover, many power converters can be configured to convert DC into AC(typically called inverters), as well as many other power conversionfunctions. Thus, DDBC 120 can, in some embodiments, be implemented by amulti-function power converter that is configured to operate as aconverter, i.e., convert DC into DC, or inverter, i.e. to convert DCinto AC, or rectifier, i.e. to convert AC into DC. However, in someembodiments, DDBC 120 is implemented by a device that can only convertDC into DC, DC into AC or AC into DC.

Turning now to FIG. 4, there is shown a more detailed embodiment ofpower conversion system 100. In this embodiment, power conversion system100 includes input terminals 132, allowing mechanical and electricalconnection to DC source 104 and the other components of the powerconversion system. At the point of power input to DDBC 120 is a sensor136, which measures an input current 140 coming from DC source 104 andtransmits a signal 144, representative of the input current, to controlsystem 128.

Input current 140 is then fed into an input current filter 148. In anexemplary embodiment, input current filter 148 is an inductor/capacitorcombination that filters input current 140 to protect DC source 104 fromthe effects of AC ripple caused by switching of transistors, e.g.,MOSFETS (high frequency), and feedback from the grid (low frequency).This AC ripple can cause localized voltage changes in electrodes, whichresults in increased fuel consumption and loss of efficiency in fuelcells, Faradaic heating in batteries and disruptions in peak powertracking algorithms, thereby leading to loss of efficiency indistributed generation devices.

In an exemplary embodiment, when DDBC 120 is configured as a pulse widthmodulated (PWM) boost converter, the DDBC receives the filtered currentinput from input current filter 148 and converts the low voltage DC tohigh voltage DC in three steps. Power conversion system 100 converts thelow voltage DC signal to a low voltage AC signal, then converts the lowvoltage AC signal to high voltage AC signal, then converts the highvoltage AC signal to a high voltage DC signal. Two, interacting controlloops are used in conjunction with DDBC 120.

Regulation of the voltage boost provided by DDBC 120 can be accomplishedusing one or more feedback or control loops. For example, and as shownin FIG. 4, a feedback loop 152 is electronically coupled to DDBC 120 andcontrol system 128. Feedback loop 152, is an inner, fast loop of powerconversion system 100, which regulates the voltage boost of thetransformers by receiving, as an input, a fixed input voltage signal,representative of the voltage on inverter 124, and adjusting the phaseangles of the voltages of the power sent from the DC source on thetransformer primary windings (discussed and shown in FIG. 5) by using,for example, phase-shifting modulation technique whose algorithms residein the microprocessor. The DC source voltage will vary based on severalvariables including: output current, level of degradation, and controlmethods such as peak power tracking (PPT) employed by the controlsystem. In one embodiment, feedback loop 152 transmits power at areference voltage from a power supply (not shown) to the transformerprimary windings to adjust the voltage phase angles seen by thetransformers; the higher the applied voltage, the lower the duty ratioof the transformers and the lower the voltage boost and vice versa: thelower the applied voltage, the higher the duty ratio and the higher theboost. In another embodiment, feedback loop 152 receives referencevoltage power from a dedicated circuit (not shown) that draws power fromDC source 104 and fixes its voltage through an additional dedicatedtransformer arrangement designed especially for this task, such as onewith primary windings connected in the delta configuration and secondarywindings connected in wye to produce a desired phase-shift.

An output current sensor 156 is coupled between DDBC 120 and controlsystem 128. Output current sensor 156 measures the current exiting DDBC120 and sends a signal 160 representative of the current to controlsystem 128.

The high DC voltage power generated by DDBC 120 is transmitted toinverter 124 (through an output current filter, such as output filter316 shown in FIG. 5) for conversion into high voltage AC suitable forintroduction to the AC load 108. The amount of power available to ACload 108 is dependent upon, among other things, the available outputcurrent of DC source 104. Control over the power draw to AC load 108 canbe accomplished using control loop 154, which is electrically coupled tocontrol system 128 and output current sensor 156. In an exemplaryembodiment, control loop 154 provides a power draw command to inverter124 based upon the available output current of DC source 104 (determinedfrom a signal received from output current sensor 156). If DC source 104cannot meet the power draw command, control system 128 de-rates powerconversion system 100. In another exemplary embodiment, control system128 can sense power demands of AC load 108 (via voltage drop or otherindication not shown) and responsively increase demand on DC source 104.In this embodiment, control loop 154 monitors output current sensor 156to ensure voltage demand is met using DC link capacitors to maintainvoltage at a level set by the microprocessor. If the voltage level isnot reached, control loop 154 signals to control system 128 that powerconversion system 100 needs to be derated.

FIG. 5 shows an embodiment of a DC-DC boost converter, DDBC 300,suitable for use in the power conversion systems described herein. Thetopology of DDBC 300 can be described as three interleaved, isolated,full-bridge DC-DC converters in a Delta-Wye configuration followed by asynchronous, three-leg bridge. In this embodiment, three phases areused. However, more or fewer phases may be implemented. Splitting theconversion into three phases allows the high current to be spread acrossmultiple legs thereby increasing efficiency and heat dissipation. Thefigure shows, first, a plurality of MOSFET-based DC-AC converters 304,e.g., 304A-C, that are electrically coupled to an input current filter,such as input current filter 148.

A plurality of transformers 308, e.g., transformers 308A-C, areelectrically coupled to the DC-AC converters, such that each transformeris coupled to one or more of the DC-AC converters. Thus, for example,transformer 308A is coupled to DC-AC converter 304A and 304BTransformers 308 convert the low voltage AC generated by converters to arelatively higher voltage AC. Typically, the number of transformers 308used in DDBC 300 corresponds to the number of converters 304. The amountof boost provided by DDBC 300 is regulated by the turns ratio of thetransformers 308: the higher the turns ratio, the higher the boost. Anundesirable side effect of increasing the turns ratio of thetransformers is higher the flux losses. However, by increasing thenumber of legs or phases, the duty on each transformer 308 is reduced,and the turns ratio and the flux losses are both lower. Moreover, byinterleaving, or summing, the legs after transformers 308, DDBC 300achieves a higher overall effective boost with minimal flux losses.Also, since the MOSFET-based topology is inherently high switchingfrequency, the high-frequency transformers 308 have the advantages ofbeing small in size and highly efficient.

Additionally, in grid-tied applications, transformers 3080 fulfill therequirement of grid isolation. Isolation requirements take two forms:power and signal. Power isolation is the minimization of DC currentinjected into the grid and is a stringent requirement of most utilities.Transformerless inverters are being introduced in Europe, which whilesmaller and lighter than their transformer-based counterparts, thesedevices suffer from lower efficiencies and additional components toprevent DC leakage onto the grid. Signal isolation is the separation ofgeneration-side measurements from the grid to ensure critical parametermeasurement accuracy. The integration of small, highly efficienthigh-frequency transformers, such as transformer 308, fulfills allisolation requirements with a topology solution whose complexity andcost is less than a transformerless topology.

The high voltage AC output by transformers 308 is fed to a correspondingnumber of synchronous rectifiers 312, e.g., 312A-C. Synchronousrectifiers 312 convert the high voltage AC from transformers 308 to highvoltage DC. In an exemplary embodiment, synchronous rectifiers 312 areMOSFET-based rectifying devices. Typically, the number of synchronousrectifiers 312 included with DDBC 300 is the same as the number oftransformers; however, more or fewer may be used. As shown in FIG. 5,three MOSFET-based synchronous rectifiers are electrically coupled totransformers 308. Before the output of DDBC 300 is provided to aninverter, such as inverter 124. it can pass through an output filter316. Output filter 316 protects the power conversion system from ACripple from the electrical grid (if so coupled). AC ripple from theelectrical grid will affect the performance of the power conversionsystem inductors, capacitors, switches and the low voltage DC source,e.g., fuel cell.

Overall, a power conversion system including DDCB 300 is based on aboost topology which features continuous output current, a voltage ratioless than one, and discontinuous input current. AC-DC converters 304 areoperated in parallel to help distribute dissipated heat, lower theswitch RMS current, and enable soft switching features. AC-DC converters304 are also interleaved in such fashion that when one phase stopsconducting current and its phase transformer freewheels, another phasestarts or already is conducting current. Current is thereby spreadacross all phases. Input current is always pulsed. A noted benefit ofthis topology is that power conversion efficiency increases as the inputvoltage decreases. This is counter to most power electronics behaviorwhich is just the opposite, conversion efficiency increases as voltageincreases due to a reduction in resistive losses. However, the topologydescribed herein requires higher performance, and therefore an increasedduty ratio on the switching devices, leading to reduced switching lossesthat outweigh an increase in resistive losses due to lower inputvoltage.

For DDBC 300, the input currents of all three phases sum, thus,depending on the operational mode the total input current could be foundeither between zero and one phase current (which is n×the outputcurrent) or between one and two phase currents; hence, the total inputcurrent resembles that of a multilevel converter. The system willinclude at least two control loops, as described above, which willregulate both the output current and output voltage.

Benefits of the average current control method are infinite DC gain,better control of inductor current, and immunity to noise. A lack ofinherent peak current capability is a disadvantage of this controlmethod, along with a limited current loop bandwidth characteristic tolinear control systems.

Power conversion system 100 as described herein greatly extends therange over which a DC source, such as DC source 104, can operate. Forexample, using power conversion system 100 enables a fuel cell system tocontinue to provide power to a utility grid closer as the output voltageof the fuel cell system decreases over time.

Control system 128 is designed and configured to manage the componentsof power conversion systems 100 (FIGS. 2 and 4) or 200 (FIG. 3) bycollecting information from inputs internal and external to the system,such as, but not limited to sensed input voltage, sensed input current,output voltage set point, and heat sink temperature. Informationcollected by control system 128 is input into programmed algorithms, setpoints, or lookup tables so as to determine operating parameters forpower conversion system 100, components, such as DDCB 120, controlsignals, feedback loops, and/or to generate external data for use inevaluating the efficiency, lifespan, or diagnosing problems with thepower conversion system. Although control system 128 is presentlydescribed as a separate component of power conversion system 100, it isunderstood that control system 128 can be dispersed among the variouscomponents described herein without affecting the function of the powerconversion system.

Turning now to an exemplary operation 400 of a power conversion system,such as power conversion system 100, and with reference to exemplaryembodiments shown in FIGS. 1-4 and in addition with reference to FIG. 5.

At step 404, measure the output voltage of the DC source, such as DCsource 104. Measurement of the output voltage may be via a sensor, suchas input current sensor 204, which is capable of transmitting a signalrepresentative of the voltage to a control system, such as controlsystem 128.

At step 408, the measurement from step 404 is compared to priormeasurement of the output voltage, an initial voltage output value (atinitial commissioning, the DC source, such as a fuel cell stack, willhave its highest beginning of life (BOL) voltage curve for poweroutput), a maximum power output value (as determined in step 420discussed below) or a predetermined set-point or threshold value. If theoutput voltage measured in step 404 has decreased below a certainpercentage (when compared to a prior measurement or the initial voltageoutput value) or has fallen below the predetermined set-point orthreshold value, method 400 proceeds to step 412; otherwise, the methodproceeds to step 416.

At step 412, a determination is made as to whether the DC source canincrease its current output so as to meet the rated power output of theDC source. If the DC source can increase its current output, the methodproceeds to step 416, if not, the method proceeds to step 420.

At step 416, current is drawn from a DC source into the power conversionsystem at a value sufficient to supply the inverter, such as inverter124, with sufficiently high DC voltage to efficiently operate theinverter. Process 400 then returns to step 404 to remeasure the outputvoltage of the DC source. Notably, use of a power conversion system,such as power conversion system 100, and especially DDBC's describedherein, can allow for a significant drop in DC source output voltage (incomparison to an initial voltage output value) and still providesufficient power to the inverter. In an exemplary embodiment, thevoltage drop from a commissioned value of the DC power source can be asmuch as 80%.

At step 420, if sufficient current cannot be drawn from the DC source toeffectively operate the inverter, it is determined whether or not thepower conversion system can be de-rated such that the maximum poweroutput of the system is based on maximum voltage sustainable by the DCsource. Sufficient current to maintain the voltage may be unavailablebecause other balance-of plant-components of the DC source, such as thestack air supply blower or the waste heat rejection loop of a fuel cellpower system, limit the output of the DC source. If the power conversionsystem cannot be de-rated, the system is removed from service.Otherwise, the power conversion system is de-rated at step 424 such thata maximum power output of the DC source is transmitted to step 408 forfurther comparisons between the actual output voltage measured in step404.

At step 428, a determination is made as to whether or not the DC sourcecan continue to supply power to the inverter in an amount suitable toefficiently run the inverter. If not, the DC source is taken out ofservice at step 432 and the DC source is replaced or recharged. If theDC source can provide a suitable power output to efficiently run theinverter, process 400 returns to step 404.

A power conversion system as described herein allows for: optimizationof a fuel cell, energy storage, and distributed generation system forefficiency, life, and cost instead of voltage output; recovery, use,and/or storage of additional power from these devices that until nowwould be unobtainable; increasing the useable life of the DC sourceportion of the system, e.g., a fuel cell stack, a battery string, asolar panel, a wind turbine, or a water turbine; allowing DC sources tobe used without an inverter stage in applications requiring high voltageDC inputs, e.g., a vehicle or other battery charger, a heater, a welder,a motor starter, a motor, a high voltage DC (HVDC) utility application,telecommunication equipment, a vehicle, a tractor and/or a marineauxiliary power, a material handling equipment; or providing additionalpower and life to improve the economics of the distributed powergeneration systems. Additionally, the bi-directional capability of thedevice allows for the implementation of low voltage battery storage,charged by relatively high power sources allowing for the employment ofreadily available, low cost, reliable energy storage systems such aslead acid battery.

FIG. 6 shows a diagrammatic representation of one implementation of amachine/computing device 500 that can be used to implement a set ofinstructions for causing one or more control systems of power conversionsystem 100, for example, control system 128, to perform any one or moreof the aspects and/or methodologies of the present disclosure. Device500 includes a processor 505 and a memory 510 that communicate with eachother, and with other components, such as DDBC 120 and inverter 124, viaa bus 515. Bus 515 may include any of several types of communicationstructures including, but not limited to, a memory bus, a memorycontroller, a peripheral bus, a local bus, and any combinations thereof,using any of a variety of architectures.

Memory 510 may include various components (e.g., machine-readable media)including, but not limited to, a random access memory component (e.g, astatic RAM “SRAM”, a dynamic RAM “DRAM”, etc.), a read-only component,and any combinations thereof. In one example, a basic input/outputsystem 520 (BIOS), including basic routines that help to transferinformation between elements within device 500, such as during start-up,may be stored in memory 510. Memory 510 may also include (e.g., storedon one or more machine-readable media) instructions (e.g., software) 525embodying any one or more of the aspects and/or methodologies of thepresent disclosure. In another example, memory 510 may further includeany number of program modules including, but not limited to, anoperating system, one or more application programs, other programmodules, program data, and any combinations thereof.

Device 500 may also include a storage device 530. Examples of a storagedevice (e.g., storage device 530) include, but are not limited to, ahard disk drive for reading from and/or writing to a hard disk, amagnetic disk drive for reading from and/or writing to a removablemagnetic disk, an optical disk drive for reading from and/or writing toan optical media (e.g., a CD, a DVD, etc.), a solid-state memory device,and any combinations thereof. Storage device 530 may be connected to bus515 by an appropriate interface (not shown). Example interfaces include,but are not limited to, SCSI, advanced technology attachment (ATA),serial ATA, universal serial bus (USB), IEEE 1395 (FIREWIRE), and anycombinations thereof. In one example, storage device 530 may beremovably interfaced with device 500 (e.g., via an external portconnector (not shown)). Particularly, storage device 530 and anassociated machine-readable medium 535 may provide nonvolatile and/orvolatile storage of machine-readable instructions, data structures,program modules, and/or other data for control system 128. In oneexample, instructions 525 may reside, completely or partially, withinmachine-readable medium 535. In another example, instructions 525 mayreside, completely or partially, within processor 505.

Device 500 may also include a connection to one or more sensors, such assensor 208 and/or output current sensor 240. Sensors may be interfacedto bus 515 via any of a variety of interfaces (not shown) including, butnot limited to, a serial interface, a parallel interface, a game port, aUSB interface, a FIREWIRE interface, a direct connection to bus 515, andany combinations thereof. Alternatively, in one example, a user ofdevice 500 may enter commands and/or other information into device 500via an input device (not shown). Examples of an input device include,but are not limited to, an alpha-numeric input device (e.g., akeyboard), a pointing device, a joystick, a gamepad, an audio inputdevice (e.g., a microphone, a voice response system, etc.), a cursorcontrol device (e.g., a mouse), a touchpad, an optical scanner, a videocapture device (e.g., a still camera, a video camera), touchscreen, andany combinations thereof.

A user may also input commands and/or other information to device 500via storage device 530 (e.g., a removable disk drive, a flash drive,etc.) and/or a network interface device 545. A network interface device,such as network interface device 545, may be utilized for connectingdevice 500 to one or more of a variety of networks, such as network 550,and one or more remote devices 555 connected thereto. Examples of anetwork interface device include, but are not limited to, a networkinterface card, a modem, and any combination thereof. Examples of anetwork include, but are not limited to, a wide area network (e.g., theInternet, an enterprise network), a local area network (e.g., a networkassociated with an office, a building, a campus or other relativelysmall geographic space), a telephone network, a direct connectionbetween two computing devices, and any combinations thereof. A network,such as network 550, may employ a wired and/or a wireless mode ofcommunication. In general, any network topology may be used. Information(e.g., data, instructions 525, etc.) may be communicated to and/or fromdevice 500 via network interface device 555.

Device 500 may further include a video display adapter 560 forcommunicating a displayable image to a display device 565. Examples of adisplay device 565 include, but are not limited to, a liquid crystaldisplay (LCD), a cathode ray tube (CRT), a plasma display, and anycombinations thereof.

In addition to display device 565, device 500 may include a connectionto one or more other peripheral output devices including, but notlimited to, an audio speaker, a printer, and any combinations thereof.Peripheral output devices may be connected to bus 515 via a peripheralinterface 570. Examples of a peripheral interface include, but are notlimited to, a serial port, a USB connection, a FIREWIRE connection, aparallel connection, a wireless connection, and any combinationsthereof.

A digitizer (not shown) and an accompanying pen/stylus, if needed, maybe included in order to digitally capture freehand input. A pendigitizer may be separately configured or coextensive with a displayarea of display device 565. Accordingly, a digitizer may be integratedwith display device 565, or may exist as a separate device overlaying orotherwise appended to display device 565.

Exemplary embodiments have been disclosed above and illustrated in theaccompanying drawings. It will be understood by those skilled in the artthat various changes, omissions, and additions may be made to that whichis specifically disclosed herein without departing from the spirit andscope of the present invention.

What is claimed is:
 1. A DC to DC boost converter (DDBC) for convertingpower received from a variable, low voltage DC source, the DDBCcomprising: a plurality of interleaved, isolated, full-bridge DC-DCconverters arranged in a Delta-Wye configuration and a multi-leg bridge;an input current filter and a plurality of DC-AC converters, whereinsaid plurality of DC-AC converters are electronically coupled to saidinput current filter and configured to receive a discontinuous inputcurrent; and a plurality of transformers, wherein each of said pluralityof transformers is electronically coupled to a corresponding respectiveone of said plurality of DC-AC converters.
 2. The DDBC according toclaim 1, wherein the DDBC has a boost ratio of greater than 5:1.
 3. TheDDBC according to claim 1, wherein the DDBC converter is bi-directional.4. The DDBC according to claim 1, wherein the DDBC conversion efficiencyincreases as the DC input voltage decreases.
 5. The DDBC according toclaim 1, wherein the DDBC has a configurable boost ration that varieswith a DCV output set point and a DCV input from the variable, lowvoltage DC source.
 6. The DDBC according to claim 1, further including acontrol system, said control system designed and configured to de-ratethe power conversion system to a lower power rating.
 7. The DDBCaccording to claim 6, wherein said control system includes a controlloop and a feedback loop, wherein said control loop monitors acontinuous current output and a discontinuous input current anddetermines a power draw command based upon said continuous currentoutput and said discontinuous input current, and wherein said feedbackloop regulates said continuous current output.
 8. The DDBC according toclaim 1, wherein each of said plurality of transformers has a turnsratio greater than 1:5.
 9. The DDBC according to claim 1, wherein theDDBC is electronically coupled to an electrical grid and said pluralityof transformers are designed and configured to provide isolation fromthe electrical grid.
 10. The DDBC according to claim 1, wherein the DDBCfurther includes a plurality of synchronous buck converters electricallycoupled to a corresponding respective one of said plurality oftransformers.
 11. The DDBC according to claim 10, wherein the combinedoutput of said plurality of synchronous buck converters is a continuousoutput current and a voltage ratio of less than one.
 12. A powerconversion system having a power rating, the power conversion systemcomprising: a low voltage power source having an initial output voltage;a DC-DC boost converter (DDBC) coupled to said power source; and aninverter coupled to said DC-DC boost converter, wherein said DC-DC boostconverter is designed and configured to provide a continuous outputcurrent, a voltage ratio less than one, and to receive a discontinuousinput current; and a control system, said control system designed andconfigured to de-rate the power conversion system to a lower powerrating, and wherein said control system includes a control loop and afeedback loop, wherein said control loop monitors said continuouscurrent output and said discontinuous input current and determines apower draw command based upon said continuous current output and saiddiscontinuous input current, and wherein said feedback loop regulatessaid continuous current output.
 13. The power conversion systemaccording to claim 12, wherein said DDBC extends the useful life of saidlow voltage power source.
 14. The power conversion system according toclaim 13, wherein said DDBC provides said continuous output current tosaid inverter when said low voltage power source has a reduced outputvoltage, said reduced output voltage being as much as about 80% of saidinitial output voltage.
 15. The power conversion system according toclaim 12, wherein said DDBC is a plurality of interleaved, isolated,full-bridge DC-DC converters arranged in a Delta-Wye configuration thatis followed by multi-leg bridge.
 16. The power conversion systemaccording to claim 12, wherein said DDBC improves power conversion ofpower from said low voltage power source as the voltage of said lowvoltage power source decreases.
 17. The power conversion systemaccording to claim 12, wherein said DDBC includes a plurality ofinterleaved, isolated, fullbridge DC-DC converters arranged in aDelta-Wye configuration and a multi-leg bridge.
 18. The power conversionsystem according to claim 17, wherein said DDBC further includes aninput current filter, a plurality of DC-AC converters, and a pluralityof transformers, wherein said plurality of DC-AC converters areelectronically coupled to said input current filter and wherein each ofsaid plurality of transformers is electronically coupled to acorresponding respective one of said plurality of DC-AC converters. 19.The power conversion system according to claim 12, wherein said lowvoltage power source is a fuel cell.
 20. The power conversion systemaccording to claim 12, wherein said low voltage power source is abattery.